Yes more than you think.
Roof box fuel efficiency.
It s impossible to give an exact figure because it depends on so many factors but britain s biggest roof box manufacturer thule states that your mpg is unlikely to decrease by more than 5.
They found that in 2015 roof racks nationwide were responsible for 0 8 percent of light duty vehicle fuel consumption or 100 million gallons of gasoline.
5 9 l 100 km 40 mpg roof mounted thule xtender 739 ski carrier with skis.
He found that compared to the baseline of no roof rack the empty rack reduced his mpg by 12 7 and the roof rack with a bicycle reduced it by a whooping 27 3.
5 6 l 100 km 42 mpg roof rack with thule dynamic 800 aerodynamic cargo box.
Do ski racks and roof boxes hurt fuel efficiency.
Adding a roof box means your car has to carve a bigger hole in the air which requires burning more fuel so your mpg will suffer.
Their study was published recently in the.
The roof rack mpg experiment he compared the gas mileage of his car at 54 7 mph 88 kph with 1 no roof racks 2 an empty roof rack and 3 a mountain bike on the roof rack.
As the british magazine what car.